Add ``Application`` support for different media.

https://github.com/madewithbytes/us_ignite/issues/134

The media could be a video hosted in a
3rd party service. e.g. YouTube.
Load initial fixtures before generating dummy content.

This makes sure that the dummy content can be generated
dinamically.
Create include for embedable media.

https://github.com/madewithbytes/us_ignite/issues/134
Validate that the URL provided can be embeded.

https://github.com/madewithbytes/us_ignite/issues/134

The only URLs supported are youtube.